How do Lenses and frames made?

The Lenses are characteristically made from one of three materials. They comprise glass, plastic (usually acrylic), and polycarbonate. Glass lenses have the finest optical clearness and scratch resistance, but are heavier than plastic or the polycarbonate lenses. They can also shatter or break on impact. The Plastic lenses are lighter than glass lenses, but are more prone to scratching. They do on the other hand, offer more resistance to shattering than glass. The Polycarbonate lenses are even lighter than plastic lenses. They are shatter-resistant (but not indestructible) making them apt for impact protection.
The Frames are normally made from plastic, nylon, a metal or metal alloy. Nylon frames are generally used in sports for the reason that they are light weight and flexible. They are able to twist slightly rather than breaking when pressure is applied to them. This flex can also help out the glasses grip well on the wearer's face. Metal frames are generally more inflexible than nylon frames thus they can be more simply damaged when participating in sporty activities, but this is not to say that they cannot be used for such activities. For the reason that metal frames are more rigid, various models have spring loaded hinges to help them grip the wearer's face better. The end of the ear pieces and the bridge over the nose can be textured or have a rubber or plastic material to hold better. The ends of the ear pieces are generally bent so that they wrap around the ear; on the other hand, some models have straight ear pieces. Oakley, for instance, has straight ear pieces on all their glasses.

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